Accidentally froze yeast

[Sadfield]

You can freeze yeast - but it's no myth that you get significant losses in viability.

For instance Park et al 1997 tested wild-type yeast (CY4) which are probably tougher than brewery yeast and found that 2 hours of freezing caused early-exponential yeast to lose ~94% of viability and late-exponential yeast to lose 40% of viability. The typical commercial pack of yeast is more like the second than the first, but that's still a big loss - and the drop is proportional to the time spent frozen, after 6 hours the 40% drop goes to >75% loss of viability.



As mentioned above, the introduction of ice crystals is the killer. If you're preparing cells for a yeast bank then a) you mix them with something like glycerol to protect them and b) you do the initial freeze by dropping them in liquid nitrogen to minimise the formation of ice crystals in the same way that Heston Blumenthal makes ice cream with liquid nitrogen to make it super-smooth, because it lacks ice crystals. Glycerol + liquid nitrogen is a long way from "just bung it in the freezer".

Sure, taking advantages of modern practices on a small number of cells. That doesn't mean that some yeast from a large collection won't survive crude practices. However, you know that, evident by the way you deliberately trunkating your quote, removing the point I made about yeast tolerating freezing in the wild. Or even in a Farmhouse brewing setting for thousands of years.

 

[Northern_Brewer]

That doesn't mean that some yeast from a large collection won't survive crude practices. However, you know that

Of course I know that it's a percentage game. But for a good fermentation you need a lot of cells - a billion cells per litre per Plato is commonly quoted although it varies a bit. So the 100 billion cells of a typical Wyeast/White Labs pack is marginal for a typical 20l fermentation even when fresh, let alone once you've killed half or more of the cells by freezing.

you deliberately trunkating your quote, removing the point I made about yeast tolerating freezing in the wild. Or even in a Farmhouse brewing setting for thousands of years.

I was merely trying to save your blushes from further demonstration of your ignorance. But if you insist, let's talk about how wild yeast survive winter and how it is not particularly relevant to a Wyeast smack pack...

Sticking a smackpack in the freezer is very different to yeast in the wild. There's lots of mechanisms they can deploy to protect themselves from stress as times get tough and food supplies dry up, by producing "antifreezes" like trehalose. But they need time and exposure to small stresses to develop those protections. It's a bit like the way that deciduous trees respond to the first frosts by dropping their leaves to protect themselves from the full stress of winter, or perhaps a better analogy is hardening off seedlings that you've germinated in your kitchen, by putting them first in a protected environment outside like a cold frame or greenhouse to give them a bit of exposure to cold-stress before planting them out in the soil. If you put them in the soil straight from your kitchen then they would die of frost, but they're OK after they've acclimatised a bit.

So it is with yeast - they also have two further tricks when in the wild, desiccating and sporulating. The ability to sporulate is one of the key survival mechanisms of wild yeast, but has been pretty much lost by domestic yeast, presumably because its nurses kept it away from extremes of heat and cold. And desiccation is not relevant when we're talking about Wyeast liquid yeast - but yes, commercial dry yeast does survive freezing much better than liquid yeast.

But all these tricks of hardening off, desiccating and sporulation do not apply to liquid brewer's yeast in a smack pack that's suddenly been thrown in the freezer without warning.

 

[Brewnaldo]

Of course I know that it's a percentage game. But for a good fermentation you need a lot of cells - a billion cells per litre per Plato is commonly quoted although it varies a bit. So the 100 billion cells of a typical Wyeast/White Labs pack is marginal for a typical 20l fermentation even when fresh, let alone once you've killed half or more of the cells by freezing.



I was merely trying to save your blushes from further demonstration of your ignorance. But if you insist, let's talk about how wild yeast survive winter and how it is not particularly relevant to a Wyeast smack pack...

Sticking a smackpack in the freezer is very different to yeast in the wild. There's lots of mechanisms they can deploy to protect themselves from stress as times get tough and food supplies dry up, by producing "antifreezes" like trehalose. But they need time and exposure to small stresses to develop those protections. It's a bit like the way that deciduous trees respond to the first frosts by dropping their leaves to protect themselves from the full stress of winter, or perhaps a better analogy is hardening off seedlings that you've germinated in your kitchen, by putting them first in a protected environment outside like a cold frame or greenhouse to give them a bit of exposure to cold-stress before planting them out in the soil. If you put them in the soil straight from your kitchen then they would die of frost, but they're OK after they've acclimatised a bit.

So it is with yeast - they also have two further tricks when in the wild, desiccating and sporulating. The ability to sporulate is one of the key survival mechanisms of wild yeast, but has been pretty much lost by domestic yeast, presumably because its nurses kept it away from extremes of heat and cold. And desiccation is not relevant when we're talking about Wyeast liquid yeast - but yes, commercial dry yeast does survive freezing much better than liquid yeast.

But all these tricks of hardening off, desiccating and sporulation do not apply to liquid brewer's yeast in a smack pack that's suddenly been thrown in the freezer without warning.

All of that aside though, on the more immediate concern of my Wyeast…. Given that it activated quickly and got going quickly in a starter, and that I intend to feed it some more starter, can I expect a normal fermentation when used do you think?

 

[Sadfield]

Of course I know that it's a percentage game. But for a good fermentation you need a lot of cells - a billion cells per litre per Plato is commonly quoted although it varies a bit. So the 100 billion cells of a typical Wyeast/White Labs pack is marginal for a typical 20l fermentation even when fresh, let alone once you've killed half or more of the cells by freezing.



I was merely trying to save your blushes from further demonstration of your ignorance. But if you insist, let's talk about how wild yeast survive winter and how it is not particularly relevant to a Wyeast smack pack...

Sticking a smackpack in the freezer is very different to yeast in the wild. There's lots of mechanisms they can deploy to protect themselves from stress as times get tough and food supplies dry up, by producing "antifreezes" like trehalose. But they need time and exposure to small stresses to develop those protections. It's a bit like the way that deciduous trees respond to the first frosts by dropping their leaves to protect themselves from the full stress of winter, or perhaps a better analogy is hardening off seedlings that you've germinated in your kitchen, by putting them first in a protected environment outside like a cold frame or greenhouse to give them a bit of exposure to cold-stress before planting them out in the soil. If you put them in the soil straight from your kitchen then they would die of frost, but they're OK after they've acclimatised a bit.

So it is with yeast - they also have two further tricks when in the wild, desiccating and sporulating. The ability to sporulate is one of the key survival mechanisms of wild yeast, but has been pretty much lost by domestic yeast, presumably because its nurses kept it away from extremes of heat and cold. And desiccation is not relevant when we're talking about Wyeast liquid yeast - but yes,

But all these tricks of hardening off, desiccating and sporulation do not apply to liquid brewer's yeast in a smack pack that's suddenly been thrown in the freezer without warning.

You appear to have lost sight of the original topic about the viability of a part frozen yeast. As you say 'commercial dry yeast does survive freezing much better than liquid yeast.' suggesting that liquid yeasts will to some degree survive freezing. Not sure what you argument is, we appear to be saying the same thing. The OPs yeast will still have some level of viability.

Yes I'm aware of trehalose, check my previous post.

 

[Brewnaldo]

Two starters later and whilst I dont have a fraction of the yeast knowledge shown by some on this thread, I can tell you in the last week I have learned that all is not lost if you freeze your yeast. I wont do it deliberately, but dont give up if you do it by mistake is the lesson